1. Field of the Invention
The invention relates to structure and manufacturing method of an SiC (Silicon Carbide) dual metal trench Schottky diode, which is applied to a Schottky diode.
2. Related Art
Regular rectifier diodes are easily switched on/off for both forward voltage and reverse voltage at low frequency operation, but the reverse voltage is not cut off at high frequency operation and finally ends up with poor rectification. The Schottky diode is usually used to solve this problem.
Referring to FIG. 1, which illustrates a cross sectional view of a conventional Schottky diode.
A conventional Schottky diodes includes ohmic contact metal 10, substrate 20, an epitaxial layer 30, and Schottky contact metal 40.
The Schottky contact metal is made of gold, silver, platinum, nickel, titanium or other metals, and the epitaxial layer is silicon material doped with impurity (normally from an N-type material). A Schottky junction is formed between the two components.
Before forward bias is applied to the Schottky diode, the energy level of free electrons in the epitaxial layer is lower than the energy level of free electrons in the Schottky contact metal. The energy difference between the two levels is called a Schottky barrier.
After forward bias is applied to the Schottky diode, the free electrons in the epitaxial layer gain enough energy so they jump over the junction and enter the Schottky contact metal and thus generate bias current. Because there is no minority carrier in the metal, thus there is no charge storage and almost no reverse recovery time.
The SiC (Silicon Carbide) Schottky diode that features the Schottky barrier and SiC material containing a high energy band gap is used to produce a high rectifier with advantages such as high voltage, high speed, and low forward voltage.
Referring to FIG. 2, which illustrates a cross sectional view of the conventional dual metal trench Schottly diode.
The dual metal trench (DMT) structure also reduces impedance and thus improves the property of the Schottky diode.
The conventional DMT Schottky diode includes ohmic contact metal 10, substrate 20, an epitaxial layer 30, Schottky contact metal 40 and a trench layer 50.
The expitxial layer 30 is etched to form opening, metal material that is different from the Schottky contact metal and is filled into the opening to form the trench layer 50.
One feature of the DMT Schottky diode is that it takes advantage of the pinch-off phenomenon occurring in the depletion area between two neighboring trench layers 50 to eliminate leakage current generated by reverse voltage.
Because of the curved equipotential line occurring in the bottom corner of the trench layer 50, a magnified electric field caused by point discharge is found in the corner. The magnified electric field reduces the Schottky barrier and then increases the leakage current. Furthermore, avalanche breakdown is also very possible in the corner.
In order to solve those conventional problems, the invention provides a structure and manufacturing method of an SiC dual metal trench Schottky diode to eliminate leakage current and increase the concentration of the epitaxial layer.
In the invention, P-type impurity is doped into the bottom of the trench layer of the dual metal trench Schottky diode to eliminate leakage current or avalanche breakdown in the corner of the trench layer in order to increase concentration of the epitaxial layer. N-type impurity can also be doped into the region between the Schottky contact metal and the epitaxial layer to adjust the Schottky barrier and thus reduce forward voltage required for current to flow through.
The SiC dual metal trench Schottky diode of the invention includes ohmic contact metal, substrate, an epitaxial layer, Schottky contact metal, a trench layer and implant. The implant formed by P-type impurity is located at the bottom of the trench layer, between the epitaxial layer and the trench layer.
The manufacturing method of the SiC dual metal trench Schottky diode of the invention includes the following steps: providing an ohmic contact metal, forming a substrate, forming an epitaxial layer, forming a Schottky contact metal, etching, forming an implant, forming a trench layer.
The object of the invention is to separate the switch controlling forward and reverse voltage in order to obtain better rectifier diode performance.
Further scope of applicability of the invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.